Hesaraghatta Catchment Timeseries Analysis

Rainfall Timeseries Analysis for 122 years (1901-2022)

Updated Date: 21 NOV 2023

The Indian Meteorological Department (IMD) defines four meteorological seasons for each year: Winter (Jan – Feb), Pre-monsoon (Mar-May), Southwest Monsoon (Jun-Sep), and Post-monsoon (Oct-Dec). In this study, we conduct a rainfall time series analysis from 1901 to 2022 for each of these four seasons and annually. The data is derived from IMD daily rainfall records.

Executive Summary:

Analysing 122 years of IMD’s rainfall data in the Hesarghatta catchment reveals that 2022 recorded the highest annual rainfall.This extends to Southwest Monsoon, where 2022 is the highest.In the case of Northeast, 2021 records the highest.In the pre-monsoon season, 2022 ranks second in terms of rainfall.The winter season characterised by minimal rainfall records 1908 as the highest, while the fifth-highest is 2021.

Executive Summary Table

1. Annual Rainfall Timeseries (1901 – 2022)

Graph 1: Annual Rainfall Timeseries (1901 -2020)

In 2022, the Hesaraghatta catchment witnessed unprecedented rainfall, setting a new record as shown in Graph 1 . The recorded rainfall of 1568mm marked a remarkable 98% departure from the Indian Meteorological Department’s (IMD) current normal of 791mm and a substantial 93% departure from the World Meteorological Organization’s (WMO) current normal of 814mm. When compared to the WMO’s historical normal of 740mm, the departure reached an astonishing 112%. It can be observed from the Table 1, which illustrates the top ten rainfall years and their respective departures, that the percentage of departures in 2022 far exceeds any other year on record.

In 1985, the driest year on record was documented with a meagre 360mm of rainfall. Graph 1 visually showcases the top five driest years.

Graph 1 also depicts the top ten rainfall years. Seven of the top ten occurred post-1990, with five occurring after 2009. Out of 122 years, 20 experienced rainfall exceeding 1000mm, with 14 occurrences observed after 1971, signalling recent intensification. This aligns with rising CO₂ levels marked on the graph, suggesting a link between climate change and changing precipitation patterns.

Table 1: Top Ten Rainfall Years and % Departures

2. Southwest Monsoon (Jun-Sep) Timeseries (1901 – 2022)

Graph 2: Southwest Monsoon Timeseries (1901 -2020)

In 2022, the Hesaraghatta catchment experienced unprecedented rainfall, reaching 918mm— a remarkable 108% departure from both IMD’s and WMO’s current normal rainfall of 441mm as shown in Graph 2 . When compared to the WMO’s historical normal of 430mm, this departure is an astonishing 114%. The accompanying table highlights the top ten rainfall years and their departures, emphasizing that the percentage departure in 2022’s southwest monsoon rainfall surpasses all others.

The driest year on record occurred in 2002, with minimal rainfall totaling just 135mm.

Table 2: Top Ten highest of Southwest monsoon and % Departures

3. Post Monsoon (Oct-Dec) Timeseries (1901 – 2022)

Graph 3: Post Monsoon (Oct-Dec) Timeseries (1901 -2020)

As shown in Graph 3, 2021 rainfall set a record at 569mm, marking a substantial departure of 172% from IMD’s current normal of 209mm and 157% from WMO’s current normal of 221mm.Compared to WMO’s historical normal of 191mm, the departure in 2021 was a staggering 198%.

1991 and 2021 are the sole years in the 122-year history with over 500mm of rainfall, with the former just 7mm less than the record-shattering 2021 rainfall. Both years exhibit significant deviations from normal, as evident in the top ten rainfall years and their departures from Table 3.

The driest year recorded was 1959, with a minimal 29mm rainfall.

Table 3: Top Ten highest of Post Monsoon and % Departures

4. Pre Monsoon (Mar-May) Timeseries (1901 – 2022)

Graph 4: Pre Monsoon (Mar-May) Timeseries (1901 -2020)

As shown in Graph 4, 2011’s record-shattering pre-monsoon rainfall is at 333mm. The second-highest was recorded in 2022 at 303mm. Both 2022 and 2011 are the only two years in the 122-year rainfall history with over 300mm.

The 2011 rainfall of 333mm marks a 159% departure from IMD’s current normal of 133mm and a 128% departure from WMO’s current normal of 145mm.

Compared to WMO’s historical normal of 110mm, the departure of 2011 rainfall is a staggering 200%.

Table 4 below illustrates the top ten rainfall years and their departures, emphasising 2011’s substantial deviation from normals.

1906 recorded the driest year with 19mm of rainfall.

Table 4: Top Ten highest of Pre Monsoon and % Departures